With the realization that chairs should be useful for persons of widely differing sizes and shapes, various attempts have been made to provide releasable locking arrangements operable to maintain an armrest in a desired position with respect to its seat in either lateral or vertical directions.
One example of such an adjustment arrangement is shown in U.S. Pat. No. 4,085,967 issued Apr. 25, 1978 to Spencer, wherein a stool including an armrest is mounted via a pair of upright supports to bearing sleeves in a bearing bracket. Short rods are fixed to the upper ends of supports and a position-maintaining unit is interposed between the rods and the armrest. The position-maintaining unit includes an actuating lever which is manually actuable for selectively enabling an operator to adjust the angle and fix supports in a desired predetermined position via a clutch arrangement to fix the front-rear position of the armrest.
In U.S. Pat. No. 455,168 issued Jun. 30, 1891 to Case, a transverse horizontal adjustment mechanism includes a channel which receives horizontal portions of arm supports or standards for sidearms. Each horizontal portion includes a rectangular slot having a series of gear teeth at one edge which constantly engages a rotary pinion extending into the channel. Adjustment of the lateral position of the sidearms is accomplished by exerting a manual force either inwardly or outwardly on one of the arms, which is transferred through the pinion to the other arm to simultaneously move both arms inwardly or outwardly.
In U.S. Pat. No. 4,884,846 issued Dec. 5, 1989 to Tobler, a horizontal arm adjustment system includes a horizontally extending support portion pivotally connected to a cross-support element which in turn is secured to the seat. To adjust the spacing between armrests, the user first loosens the support braces from one of the screw holes, repositions the support braces as desired to the other holes, and then reattaches the braces.
In U.S. Pat. No. 3,586,374 issued Jun. 22, 1971 to Laessker, there is disclosed a system for horizontally adjusting the armrests which is mounted to a first sleeve which is, in turn, received within a second sleeve having a series of internal detents. An actuator rod extends through the first sleeve for selectively moving a ball into and out of engagement with the detents upon inward and outward movement of a rod. A spring biases the rod outwardly for forcing the ball into engagement with one of the detents.
In U.S. Pat. No. 413,156 issued Oct. 15, 1889 to Wilkerson, a dental chair includes a horizontal adjustment system in the form of a slot formed in the portion of an arm mounting bracket extending under the seat and a set screw having a handle extending through the slot for selectively adjusting the horizontal position of the arm.
Notwithstanding these previous designs, it remains desirable to provide a leveraged clamping adjustment mechanism of a different type from that shown in the aforementioned prior art which is easily adjusted, positively locked, quickly released, and virtually maintenance free. It is also highly desirable that such adjustment mechanism is economical to manufacture and easy to assemble.